The7Stars was awarded the account without a pitch. Gymbox worked with Frank PR on media for its most recent campaigns.
This first outdoor campaign targets ABC1 18- to 35-year-olds, and promotes the five luxury Gymbox fitness clubs in London.
The work will launch on Monday 13 January and will appear in large-format outdoor sites, as well as smaller six-sheet formats close to Gymbox gyms, competitor gyms and areas with heavy footfall.
The creative work was by the Karma Communications Group youth agency Kid, and features toned bodies cut below the neck. Bold type over them spells out phrases commonly used in gyms, such as "knockout" and "hardcore", playing on their sexually suggestive nature.
David Cooper, the brand and product director at Gymbox, said: "We wanted a big, bold and hard-hitting campaign and the7stars is the perfect partner to get our message across.
"The well-placed ads use common gym phrases in a humorous and smart way, and we are looking forward to seeing the reactions of both members and non-members of Gymbox."
The campaign will run until March.
Ellie Ring, a senior account manager at the7stars, said: "The playful nature of the Gymbox advertising suits the ethos of the7stars perfectly and we have ensured it will hit the target market with real force in the New Year and throughout."